Hydraulic cement compositions

ABSTRACT

A hydraulic cement composition comprising a uniform, finely divided mixture of a Portland cement and mineral wool shot slag, the proportion of slag being from about 10 to 90 percent by weight of the mixture.

X 1/ 1 AU 1 12 E 2 327 GR 396159783 Inventor John Wilfred Howard [56]References Cited 164 North Shore Boulevard East, UNlTED 51' ATES PATENTSA I No 2,230,103 1/1966 Minnick 106/117 f J 24 1970 2,987,407 6/1961Ulfstedt et a1. 106/97 2,815,293 12/1957 11111166116131. 106/97 PatentedOct. 26, 1971 2,588,248 3/1952 Klein 61/36 2046142 6/1936 wm 106/117 629420 Apr. 10 1967 now abandoned. y

844,530 2/1907 Mollenbruck 106/93 OTHER REFERENCES HYDRAULIC CEMENTCOMPOSITIONS Taylor, W. H. Concrete Technology and Practice," AmericanElsevier, p. 175 (1965).

Primary Examiner-Tobias E. Levow Assistant Examiner-W. T. ScottAttorney-Thomas B. Graham HYDRAULIC CEMENT COMPOSITIONS RELATEDAPPLICATION BACKGROUND OF THE INVENTION Most concrete throughout theworld is made with some form of fine and coarse aggregates such as sandand gravel respectively and some type of hydraulic cement, (the Portlandcement being by far the most prevalent in England and America), waterand frequently, in modern times, with one or more beneficial admixtures.The cements so used are termed hydraulic cemenB" because the particleschange profoundly in the presence of water so causing the cementing ofthe aggregates into a monolithic mass.

The strength of the mass after an appropriate time under favorableconditions, depends to a large extent on the hydraulicity" of thecement-its ability to change particlecharacter in water. To be morespecific, Portland cement is made from high lime content rock and clayor shale, pulverized and mixed. Neither of these ingredients has anyhydraulicity even after pulverizing, until burned in a kiln andrepulverized to suitable fineness, whereupon they become Portlandcement. It will be noted that it is a product of an intense heatprocess; when hydrated later to enable it to form concrete, it liberatesconsiderable heat in the transformation, and such heat, while it may beignored, or be useful in much construction work, can be extremelytroublesome in large masses of concrete from which the heat cannotescape as fast as it is generated, and therefore raises the temperatureof the mass dangerously high. All cements vary with respect to eachother in this tendency, and a low heat" type must often be specifiedeven at additional cost.

Iron blast furnace slag, if it has suitable chemical content, may beuseful in making cement. It is a byproduct of the smelting process and,as discharged from the smelter, is a molten liquid comprising thenonmetallic elements of the iron ore and the lime rock which isnecessarily added to the smelter as a flux." Normally it cools in theair in a convenient dumping place, hardens and is known as air-cooledhard iron blast furnace slag." It can be crushed into concrete aggregateand, being a product of heat, tends to make concrete heat resisting whenused in such concrete as aggregates. It can also be ground and usedlargely or in some lesser proportion in place of lime rock as rawmaterial in manufacture of Portland cement. It may be cooled morerapidly with the aid of water and so converted to expanded" slag, usefulin concrete as lightweight and insulating aggregate. It has nohydraulicity or cementitious properties in either form above. Except forits typical porosity it resembles somewhat natural rock and its particlestructure is called "crystalline."

Over 100 years ago it was found that if slag were cooled with abnormalrapidity with the aid of water it would be convened to a more or lessvitreous (glassy)state, and in so doing, formed into small particlesresembling sand. This came to be generally known as granulated" slag todifferentiate it from air-cooled hard slag and it has little resemblanceto hard slag pulverized to the same particle size. though it would havethe same chemical content. Granulated slag was found capable ofcementing itself into a mass if exposed to moisture and this was foundto be due to what had to be termed the latent" hydraulicity of the glassparticles, inert in themselves but, activated by the element of freelime which was necessarily also present because the granulation processnever produced an entirely vitreous product. The finer the particles thestronger the cementing action observed. Such material pulverized to acontrolled fineness and proportioned with lime is called Slag Cement."

Since the discovery of the latent cementitious properties of glassyslag, research scientists have been endeavoring to discover the bestactivators to realize its latent strength properties. The following arethe main combinations of materials found successful in this connection:

1. What is called "Slag Cement" or "Slag Lime Cement" which ispulverized granulated slag comprising at least 60 percent by weight ofthe total with not more than 40 percent hydrated lime. it is definedsubstantially as above in the latest ASTM specification C595-68. It isrelatively cheap, but needs to be very finely ground, and its strengthrequirements are the lowest of the various types of cement.

2. Supersulfate Cement" is composed of 80-85 percent of granulated blastfurnace slag, the remainder being calcium sulfate (gypsum) with a smallamount of lime. It is capable of high-strength development, highresistance to sulfate-contaminated water, low heat of hydration,moderate resistance to acid and high resistance to attack by sea water.

3. IPortland Blast-Fumace Slag Cement" or Portland Blast Furnace Cement"is defined in thTlifZst ASTM specification C595-68 as: "The product ofintimately intergrinding a mixture of Portland cement clinker andgranulated blast furnace slag. The amount of granulated blast furnaceslag used, is such that the slag constituent makes up between 25% and65% of the Portland blast furnace slag cement by weight." A note to theforegoing addition adds, The attainment of an intimate and uniform blendof Portland cement and fine granulated blast furnace slag is difficult.Consequently, adequate equipment and controls must be provided by themanufacturer. The

purchaser should assure himself of the adequacy of the blendingoperation."

In the publication referred to above, granulated slag is defined as,"the nonmetallic product consisting essentially of silicates andalumino-silicates of calcium which is developed simultaneously with ironin a blast furnace and is produced by quenching the molten material inwater or in water. steam and air."

Before considering the novel process which constitutes the presentinvention, US. Pat. No. 2,687,996 to Trief of Aug. 3 l I954 appears tosuggest the grinding of granulated slag in the wet condition instead ofdry as Portland cement is necessarily ground. lt is repeated howeverthat if slag be I00 percent pure glass and has not hydraulicity initself, it could be ground wet. in distilled water without danger ofhardening until later combined with the intended activator agenthavingregard to the fact that hard water contains minute quantities ofactivator for slag. It would appear however that the Trief patent onlyteaches the principle of briqueting the ground wet slag so that the samemay be preserved in storage for later use. whereas it could not beadequately preserved in wet storage as a slurry due to the danger of itshardening in a mass in the storage tank or silo. The reason for thedanger of such hardening is that is cannot be depended upon to be pureglass. The normal granulation process as carried on at the blast furnaceby quenching with water, rarely contains percent glassiness; the residuenormally contains free lime and it is the ideal activator, alreadyplaced in action in the presence of water before it is desired inaction.

The present inventor is also cognizant of The Chemistry of Cement andConcrete by the highly respected authorities Sir Frederick M. Lea and C.H. Desch, in which it is stated that:

I The granulation of the blast furnace slag has been the subject of alarge number of patents but the methods employed are usually quitesimple. There are three main processes which have been used, water,steam and air granulation. In the water granulation process, the moltenslag is allowed to run into a sheet-iron through into which a stream ofwater under high pressure is introduced. The slag is broken up intosmall particles and the mixture of slag and water is run into truckswith a perforated floor to allow the excess water to drain off. Thesuccess of the process depends on bringing the slag into contact withthe water as soon as possible after it has left the furnace, and using asufficiently rapid stream of water to granulate the slag immediately itenters the trough. A jet of water is often used to play on the slag justas it enters the trough. In another method the slag stream is run into alarge tank of water and a jet of cold water arranged to play on it as itenters. The granulated slag is removed from the tank by bucketelevators. Various other methods, such as rotating steel drum onto whichthe slag impinges and water is sprayed, have also been 'used. There arealso various special processes for the introduction ofsalts into theslag during granulation.

The water-granulated slag contains from to 40 percent water and is driedin rotary driers by waste blast-furnace gases. The steam and airgranulation processes have been used to avoid the high costs of dryingthe water-granulated slag. In one such process a jet of high-pressuresteam impinges on the falling slag and effects the granulation. inanother method the slag is run on to a revolving steel plate which isprovided with steam jets. A revolving drum has also been used; the wallsare water-cooled and the slag is projected against them by means of dampcompressed air. The Buderus process utilized a combination of an airblast and a water spray which was so regulated as to produce a dryproduct.

The object of granulation is to obtain the slag in as glassy andnon-crystalline condition as possible. Slags very high in lime requiremuch more intensive cooling than those somewhat lower in lime, and aprocess which may work satisfactorily with one slag may not besufficiently rapid in its effect to granulate another successfully.While the air and steam granulation processes have been usedsuccessfully on suitable slags, and the hydraulic properties are thenequal to those of water-granulated slags, most works now use awatergranulation process."

SUMMARY OF THE INVENTION It isthe primary object of this invention toprepare a cement product which exhibits superior hydraulic cementitiousproperties.

It is a further object to utilize mineral wool shot slag in thepreparation of this superior cement product, such slag having previouslybeen recognized as useless for cement applications.

Various objects and advantages of this invention will become apparentfrom the following detailed description thereof.

The present invention consists of a method of producing a new hydrauliccement, useful in concrete and in masonry mor tars, by utilizing themodified iron 'blast furnace slag available as a byproduct of themineral wool manufacturing industry, in combination with conventionalPortland cement.'Such slag, by virtue of its modification, is decidedlymore purely vitreous than it can otherwise normally be produced, andaccordingly is capable of producing better cement than can conventional,unmodified iron blast furnace slag. The slag aforesaid which is abyproduct of the mineral wool manufacturing industry is modified by theaddition thereto of silicon dioxide, and alumina or an oxide thereof sothat it constitutes a slag with a ratio ofsilicon dioxide substantiallyhigher than lime, and such has not previously been found useful forcement. From what has just been stated, it will be appreciated that theaforesaid byproduct, generally known as mineral wool shot or shot slagis in fact conventional iron blast furnace slag enriched by the juststated ingredients and proportionately impoverished in its lime content.

DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of this invention.the term modified slag cement refers to hydraulic cement prepared eitherby blending finely divided modified slag with Portland cement or byintergrinding modified slag with Portland cement clinker to a finelydivided state.

Although this specification will make reference to only one variety ofPortland cement, it is to be noted that all commercially availablePortland cements are applicable for use in the novel hydraulic cementcompositions of this invention. Furthermore, the resulting cementsexhibit improved properties regardless of the Portland cements utilizedtherein.

Mineral wool was formerly made from lime rock or dolomite. Within thelast 25 years, however, slag has been used in its place. The byproductof both the said dolomite, and slag has been considered useless andhence wasted according to the information of the present inventor. ithas already been indicated that, essentially, mineral wool or bulk glassfiber is made from iron blast furnace slag resmelted with the additionof silicon dioxide and alumina or an oxide thereofin some way introducedwhereby it is to be found in the mineral wool shot byproduct. In themanufacture of mineral wool, approximately half of the just-namedproduct is produced from the volume of iron blast furnace slag smeltedfor the production thereof. The remaining half is the mineral wool shotor shot slag, whose virtue, in the manufacture of superior cements isherein recognized. The slag is propelled from the furnace under theinfluence of steam. The mineral wool fiber and the shot slag are airchilled during the course of propulsion from the furnace. The shot slagbeing globular (hence the name) is precipitated, while the acceptablemineral fiber remains airborne until picked up and collected foreventual use as "mineral wool. Apparently, what governs the potentialhydraulic cementitiousness of slag is not its chemical compositionprimarily, but its vitreous state. This is believed by the inventor todepend partly upon the chemical composition, but largely upon thetemperature of the melt, and promptness of its sudden chilling before anundesirable drop in the melt temperature occurs.

By analysis, mineral wool shot has been found to be constituted of thefollowing ingredients in the following amounts: silicon dioxide (SiO,)42.10 percent; alumina (Al,0,) 9.ll percent; sulfur 0.64 percent; iron(in total) 0.55 percent; lime (CaO) 34.00 percent; magnesium oxide (MgO)12.6 percent and manganese (Mn) 0.30 percent, approximately.

in view of all the foregoing the present invention should be recognizedto reside in the usage of the byproduct most usually known as mineralwool shot, or shot slag, of the mineral wool insulation manufacturingprocess, for fine grinding of such slag into a material having latenthydraulic cementitious properties. Such slag, having an approximateratio of 55:45 of silicon dioxide and lime respectively, has heretoforebeen universally recognized as useless for cement work but has beenfound by the inventor in contrast to all prior belief to have excellentlatent hydraulic cementicity. The reason for this is somewhat obscure.Nevertheless it a ears be ond rez sp ubt to the inventor elated to thelassiness of the shot slag, which Ltually mm glass, the state alwayssought for and rarely attained as wilFhEi/e appeared from the foregoingdiscussion in the slag granulation industry.

As previously indicated, mineral wool shot slag is a new and differentingredient in the making of hydraulic cement such as is used in concreteand masonry mortars. It is a new use of a longknown substance producedin large quantities. It is the first and only use known for a substancehitherto thought useless.

Advantages consequent upon the discovery ofa use, hence necessarily anew use, for mineral wool shot slag comprise:

l. the availability of an abundant new source useful in making hydrauliccement.

2. the ability to make a cement which while ground to appropriatefineness, and mixed with normal Portland cement, imparts superiorhydraulic cementitious properties which the normal Portland cement alonedoes not possess.

3. The ability to store an ingredient for making normal Portland cement,for long periods either as raw material, or when fine ground withouthardening, and indoors, or uncovered outdoors, since it is unaffected byaqueous media due to being virtually 100 percent glass, completelydevoid of free lime. and hence having no cementitious properties in orofitself.

4. The possession, due to being high in silica, low in lime. andvirtually free of tricalcium aluminate, of a lower heat hydration, andthe ability to resist acid and sulfate attack better than do cementsfalling within conventionally accepted chemical content.

5. Conformity to all ASTM (American Society for Testing Materials)standards for hydraulic cement, including preeminent performance in thesoundless autoclave expansion and contraction test, in which it had anexpansion of only 0.04 percent.

6. The ability to make whiter concrete than does normal Portland cementwithout its inclusion, due to the absence of free iron in the groundmineral wool shot.

7. The ability with equivalent workability to permit the use of a lowerwater: cement ratio than does normal Portland cement, thus contributingto impermeability and durability as accepted in concrete technology.

8. The absence of regression in many tests, including blends withseveral different Portland cements, at all ages tested less than and inexcess of 1 year.

9. Recognition of the practicability of deliberately manufacturing theslag now used primarily to manufacture mineral wool, for blending withhydraulic cement, having regard for the fact that the expensive stepsrequired primarily to produce mineral wool would be eliminated, and theentire output of the blast furnace would be air-cooled, in contrast tothe production of granulated slag which requires steam or water in itsproduction, and consequent high drying and handling costs.

The slag and the Portland cement are blended into a dry mixture in whichthe proportions of said slag are between approximately l0 percent and 90percent, by weight, ofsaid mixture. It is noted that as little as a l0percent slag modification on Portland cement provides a substantialincrease in the strength of the mortar as contrasted with 100 percentPortland. Likewise, the fact that 100 percent modified slag withoutPortland was useless in strength development indicates that the modifiedslag requires some element of Portland to act as a catalyst in order torealize its cementitious properties.

The specific gravity of the modified slag is approximately 2.90 ascompared with approximately 3.14 for Portland cement. This leads to theobvious conclusion that, when proportioned by weight, the blends of slagwith Portland are relatively rich in the absolute volume of thecementitious factor. This produces the effect that when blended, forexample, 50:50 slag to Portland by weight, the mixture is 4.25 percentricher in its blended cementitious component in terms of absolute volumeof cementitious particles. Such an increase in cement in a mix of mortaror concrete would normally, if not accompanied by an increase in waterrequirement for a given consistency, produce an increase in compressivestrength of 8 to 10 percent as has long been recognized by the law ofthe water cement ratio as laid down by Mr. Dufi Abrams half a centuryago. Accordingly, it is acknowledged that part of the superiority of thevarious blends of modified slag with Portland is attributable to thisenrichment of the cementitious factor in the mix, but this in no waydetracts from the virtue of the modified slag as it is purchased, as rawmaterial, by weight, it is processed in grinding on the basis of costper unit of weight and is blended in cement by weight.

All of the modified slag blends tend to retard the initial set of themortar or concrete as compared with the setting time of Portland and thegreater the proportion of slag the more pronounced is the retardation.Retardation of set is a desirable feature in cement in many situationsas it provides an extension of time for workability and is sometimesprovided with the aid of admixtures at extra cost. Accordingly, theblends which are richer in slag are primarily useful in this respect aswell as being very attractive economically because of the lower cost ofthe slag.

All of the modified slag blends are significantly more workable than theequivalent mix with Portland only and the richer in proportion of slagthe more pronounced is this superiority of workability.

The modified slag is present in the cements in a fineness ranging fromabout 2,000 to 7,630 Blaine, and preferably from about 4,500 to 5,600Blaine. Inasmuch as the coarser grinds yield somewhat lower strengthsthan do the finer grinds, their use is generally limited to thosesituations where strictest economy is sought in production costs andwhere early strength is immaterial. Conversely, the very fine grinds arecostly to produce and are utilized in situations where exceptionallyhigh strengths are essential.

There are various curing techniques either for use in the laboratory orin commercial concrete construction practice, which are useful,convenient and favorable to the ultimate quality of the concrete. It isunderstood, of course, that we are referring to the concrete made withhydraulic cements, including the modified slag cement. Such techniquesinclude:

a. Moist curing at lowered temperatures, from 73.4 F. down toapproximately 40 F. Under this condition most hydraulic cements developstrength more slowly than at 73.4 F. but ultimately attain a higherlevel of strength and, in this respect, the modified slag cement provedby test to be no exception.

b. Moist curing at elevated temperatures (and at atmospheric pressures)from 73.4 F. to 212 F. as is often employed in precast concreteindustries, the usual temperature range being from 150 to 200 F. In thiscase, the concrete develops strength much more rapidly than at lowertemperatures but seldom attains as high a level of ultimate strength asit does with cooler curing. Again the modified slag cement proved bytest to conform generally to the behavior of other hydraulic cements.

c. Dry curing at ordinary temperatures has virtually never been foundfavorable to strength development of any hydraulic cement. it normallyaccelerates early strength development but sharply inhibits ultimatestrength as compared with moist curing. The modified slag cement alsoconforms in this respect, it being capable of strength development in adry environment but at a significantly lower level than it is capable ofin moisture. It actually exceeds Portland cement in dry curing but doesnot exceed it by as great a margin as it does in moisture, compared withPortland also cured in moisture.

d. Autoclave curing is the method of curing in steam at elevatedtemperatures and elevated pressures in pressure vessels. While thepractitioner may select the temperatures and pressures best suited tohis needs and his particular cement system, 365 F. at 150 p.s.i. steampressure for a duration of 5% hours is typical for testing purposeswhile lower temperatures (350 to 360 F.) with proportionately lowerpressures (140 to I48 p.s.i.) and sometimes for shorter duration (3% to4% hours) are usually employed in the concrete block industry. It is astandard method of curing to which all hydraulic cements are expected toreact favorably, including the Portland Blast Furnace Slag type ofcements.

The latter autoclave-curing technique represents a novel departure fromtypical cement curing procedures. Thus, such a technique enhances thecompression strength of the resulting cements. Furthermore, the modifiedslag blends with from 45 to percent slag provide a very usefulcementitious binder for autoclaved concrete products and at aconsiderable cost-saving over Portland cement.

The following examples will further illustrate the embodiments ofthisinvention.

EXAMPLE I This example illustrates the advisability of adhering to theslag concentrations specified herein in preparing the operativehydraulic cements of this invention.

Hydraulic cements were prepared by uniformly blending 5,440 Blainefineness modified mineral wool shot slag with normal (ASTM Type I)Portland cement in a variety of component proportions. Test specimens ofeach of the cement blends were formed into 2-inch mortar cubes and curedby a moist curing technique conducted at 73.4 F. The compressivestrength of the sample cubes were determined at various intervals ofmoist curing by means ofASTM Test C-l09.

The results of these determinations are presented in the followingtable:

7 TABLE] Compressive Strength 70. by weight of (p.$.1.)21

The results presented above clearly indicate the wide range of slagconcentrations whicl't' are useful in preparing improved hydrauliccements in accordance with this invention.

EXAMPLE 11 TABLE II Compressive .Strength Blaine fitness ol ModifiedSlag (p.s.i.) at Moist Curing Interval of 3 days 7 days 28 days 3 mos.

The results presented above clearly illustrate the wide variety of slaggrinds which are useful in preparing improved hydraulic cements inaccordance with this invention.

EXAMPLE Ill This example illustrates technique of this invention.

Hydraulic cements were prepared by uniformly blending 5,400 BlaineFineness modified mineral wool shot slag with normal (ASTM Type 1)Portland cement in a variety of component proportions. The compressivestrength of the resulting cements were then determined according to theprocedure set forth in example 1 with the exception that the mortarsamples were cured by being autoclaved for a period of 5% hours at atemperature of 365 F. and a pressure of 150 p.s.i.

the novel autoclave-curing The results of these determinations arepresented in the following table:

TABLE 111 i. by weight.

of modified slag Compressive strengrhlpsi.)

0% 4.390 (i.e. 100; Portland) (all slag. no Portland) 000 (no strength)The results summarized above clearly illustrate the generalapplicability ofthis novel autoclave-curing technique.

The above described procedure was then repeated with the exception that4,800 Blaine fineness slag was substituted for the 5,400 Blaine finenessslag utilized therein. The properties of the resulting cement. andparticularly the strength. were comparable to those of the cementprepared with the liner grind slag.

Summarizing. it is seen that this invention provides novel.high-performance hydraulic cement compositions. Variations may be madein proportions. procedures and materials without departing from thescope of this invention as defined by the following claims.

What is claimed is:

1. A composition of matter which consisting essentially of a uniformmixture of Portland cement and mineral wool shot slag all reduced to afinely divided state. in which the mineral wool shot slag acts as acement upon hydration of the mixture. the proportion of slag being fromabout 10 to 90 percent by weight, of the mixture and the ratio ofsilicon dioxide being substantially higher than lime in said slag.

2. The composition of claim 1. wherein the proportion of slag in saidmixture ranges from about 25 to 65 percent. by weight.

3. The composition of claim 1. wherein the silicon dioxidezlime ratio insaid slag is 55:45.

4. The composition of claim 1. wherein the slag present in the mixturehas a 2.000 to 7.630 Blaine fineness.

5. A process for the production of a hydraulic cement product whichcomprises the steps of l. uniformly and intimately blending finelyground mineral wool shot slag with Portland cement. said slag beingpresent in the mixture in a concentration of from about 10 percent to 90percent. by weight. and having the ratio ofsilicon dioxide substantiallyhigher than lime therein;

2. hydrating the dry mixture with water;

3. casting the hydrated cement into a mold; and

4. curing the cast cement by subjecting it to steam at elevatedtemperatures and pressures in a pressure vessel.

6. The process of claim 5, wherein the proportion of slag in saidmixture ranges from about 25 to 65 percent. by weight.

7. The process of claim 5. wherein the silicon dioxidezlime ratio insaid slag is 55:45.

8. The process of claim 5. wherein the slag present in the mixture has a2.000 to 7.630 Blaine fineness.

9. The process of claim 5. wherein the curing step is conducted attemperatures ranging from about 350 to 370 F.. and at pressures rangingfrom about to pounds per square inch.

10. The process of claim 5, wherein blending step (1) consists ofintergrinding mineral wool shot slag with Portland Cement.

i 0 l I i

2. hydrating the dry mixture with water;
 2. The composition of claim 1,wherein the proportion of slag in said mixture ranges from about 25 to65 percent, by weight.
 3. The composition of claim 1, wherein thesilicon dioxide:lime ratio in said slag is 55:45.
 3. casting thehydrated cement into a mold; and
 4. curing the cast cement by subjectingit to steam at elevated temperatures and pressures in a pressure vessel.4. The composition of claim 1, wherein the slag present in the mixturehas a 2,000 to 7,630 Blaine fineness.
 5. A process for the production ofA hydraulic cement product which comprises the steps of
 6. The processof claim 5, wherein the proportion of slag in said mixture ranges fromabout 25 to 65 percent, by weight.
 7. The process of claim 5, whereinthe silicon dioxide:lime ratio in said slag is 55:45.
 8. The process ofclaim 5, wherein the slag present in the mixture has a 2,000 to 7,630Blaine fineness.
 9. The process of claim 5, wherein the curing step isconducted at temperatures ranging from about 350* to 370* F., and atpressures ranging from about 140 to 155 pounds per square inch.
 10. Theprocess of claim 5, wherein blending step (1) consists of intergrindingmineral wool shot slag with Portland Cement.